1. Field of the Invention:
The present invention relates to an apparatus for controlling arm movement of an industrial vehicle having at least two arms the movement of which is controlled.
2. Description of the Prior Art:
The present applicant has earlier proposed an industrial vehicle for foundation work (hereafter referred to as an industrial vehicle) as shown in FIGS. 9A and 9B. The industrial vehicle has a No. 1 arm 1, a No. 2 arm 2, and a No. 3 arm 3 articulated with each other as well as a first cylinder 4, a second cylinder 5, and a third cylinder 6 for driving these arms. An operating attachment such as a vibro-hammer 7, an auger drill unit 8, or the like is installed at a tip of the No. 3 arm 3. In FIGS. 9A and 9B, reference character PL denotes a sheet pile, and DR denotes an auger drill.
When such an industrial vehicle is used to drive in a sheet pile PL using the vibro-hammer 7 or bore a hole by rotating the auger drill DR by means of the auger drill unit 8, there are cases where the sheet pile PL becomes broken and the drill DR becomes damaged unless the tip of the No. 3 arm 3 is operated vertically with respect to the ground. For this reason, an assistant must be stationed in the vicinity of the industrial vehicle to visually confirm the horizontal deflection of the tip of the No. 3 arm 3 and signals the operating direction of the arm to the operator, so as to ensure, for instance, that the sheet pile PL is driven in as vertically as possible with respect to the ground.
An apparatus for controlling a position of a tip of an arm (hereafter referred to as an arm movement controlling apparatus) is conventionally known which is applied to a hydraulic power shovel having a shovel body, a boom, an arm, and a bucket installed at a tip of the arm and which is capable of controlling the position of the rotating point of the bucket in a desired direction. For instance, in the arm movement controlling apparatus known through Japanese Patent Publication No. 45025/1986, in order to control the position of the rotating point of the bucket, the targeted rotating speeds of the boom and the arm are respectively calculated by using signals from levers for controlling the speeds in the horizontal and vertical directions at the rotating point of the bucket. The flow rates of cylinders for driving the boom and the arm are controlled by using the signals thus calculated, thereby moving the rotating point of the bucket along a targeted locus (a targeted path).
However, when the movement of the tip of the No. 3 arm 3 is controlled by a manual operation in the former industrial vehicle which is not provided with the above-described arm movement controlling apparatus, the following problems are encountered:
(1) Since the horizontal deflection of the tip of the No. 3 arm 3 is confirmed visually, it is difficult to obtain desired positional accuracy with respect to the targeted locus.
(2) The operator must operate three operating levers for controlling the respective cylinders in accordance with the instructions of the assistant, so that the operating efficiency declines.
If the arm movement controlling apparatus disclosed in Japanese Patent Publication No. 45025/1986 is applied simply as it is to the above-described industrial vehicle in order that the tip of the No. 3 arm of the industrial vehicle moves along the targeted locus, the following problems are encountered:
(1) In the case of the arm movement controlling apparatus of the above publication, when the arm is controlled to move in the vertical direction, targeted angular velocities of the boom and the arm are calculated from the set value of the vertical velocity given by the lever and the value of the horizontal velocity being set to zero. However, since the positional feedback related to the position of the tip of the arm is not given, even if an error arises in the horizontal direction of the tip of the arm, it is impossible to compensate for the same. In particular, when the arm movement is controlled by driving cylinders using pressure oil whose flow rate is regulated by a solenoid proportioning valve as in the case of a hydraulic industrial vehicle, there are variations in the flow-rate characteristics of the solenoid proportioning valve itself in a low-flow-rate region, so that the arm movement controlling apparatus cannot be simply applied to an operation for which highly accurate vertical movement is required as in the case of the aforementioned operation of driving in of the sheet pile.
(2) In the above-described publication, feedback of the angular velocities are provided in a flow-rate controlling system in order to reduce such horizontal errors. However, since the velocities of movement of the rotating point of the bucket along the targeted locus in an execution operation such as the driving in of the sheet pile are slow, the angular velocities, e.g., values of differential of the arm and boom angle detected by angle detectors become very small, so that the feedback of the angular velocity does not lead to an accuracy of the position of the rotating point of the bucket to high degree.
In the arm movement controlling apparatus described in the above-described publication, the control of the vertical movement (horizontal veclocity=0) is effected by operating a boom lever alone, the control of the horizontal movement (vertical velocity=0) is effected by operating an arm lever alone, and the control of the diagonal movement is effected by operating the boom and arm levers simultaneously. With respect to this control of the diagonal movement, the control of movement in the direction of 45 degrees would be possible if the two levers are operated at the same velocity. However, the control of movement in a desired direction is difficult since the two levers must be constantly operated at a specified ratio of velocity. To overcome the difficulty of this operation, it is conceivable to provide an arm movement controlling apparatus in which a constant K is input arbitrarily by a device for setting the direction of the target locus along which the tip of the arm is controlled to be moved, and in which not only the vertical velocity but also the horizontal velocity given by a (K.times.vertical velocity) are imparted by operating the boom lever alone. However, in an operation in which, for instance, the sheet pile is driven into the ground by means of the vibro-hammer suspended from the tip of the arm, unless the starting direction of driving in the sheet pile coincides with the direction of the targeted locus predetermined by the input of the aforementioned constant K, undue forces are applied during driving in, possibly resulting in the breakage of the sheet pile.
Furthermore, when a locus control in which the tip of the arm is moved along the targeted locus is performed in an industrial vehicle having, for instance, three arms articulated with each other, if the three arms are driven simultaneously, it is impossible to perform the locus control. Therefore, the locus control has conventionally been performed under the condition of restricting movement of any one of the arms. For this reason, in cases where the amount of movement of the tip of the arm is large during the locus control as in the case of the driving in of an elongated sheet pile (i.e., in a case where the operating range is wide), it is necessary to suspend the operation temporarily midway in the operation and then to resume it after altering the posture of the arm of which movement has been restricted, thereby to perform the locus control over the entire operating range. As a result, there has been the drawback of deteriorated operating efficiency.